In recent years, many composite materials have played important roles in various fields. Many of such composite materials are produced by forming a composite of a matrix such as plastic or rubber and an additive called a filler. Regarding the filler, there is a demand for development of very light and fine filler that can contribute to resource saving and energy saving more than ever. This is because there has arisen a problem worldwide such as global warming or a rise in price of petroleum resources. As a light filler, a hollow balloon made of a material such as an organic polymer, ceramics, and/or carbon has been already developed.
Examples of a method for producing the hollow balloon (hollow carbon fine particles) are disclosed in Patent Literatures 1 to 3. Patent Literature 1 discloses thermal decomposition of thermo-plastic resin fine particles to which activated carbon powder is attached. Patent Literature 2 discloses deposition of hollow fine carbon having a non-graphite structure from carbon evaporated by thermal plasma. Further, Patent Literature 3 discloses thermal treatment of a carbon black having a specific form at a temperature of 2000° C. or more. In addition to the methods for producing the hollow carbon fine particles disclosed in Patent Literatures 1 to 3, Non-Patent Literatures 1 to 4 are reported as scientific papers.